U.S. Pat. No. 4,832,463 entitled "Thin Film Ion-Conducting Coating" describes durable, thin film ion-conducting coatings formed on a transparent glass or plastic substrate by the controlled deposition of lithium tantalate or lithium niobate. The coatings provide durable ion transport sources for thin film solid state storage batteries and electrochromic energy conservation devices.
When subjected to a low voltage pulse of a first polarity, electrons are transferred through the first outer electrode layer into the electrochromic layer cathodically coloring the layer and providing the long wave reflective state for heat reflectors. At the same time, to ensure charge compensation, there is a transfer of positive ions from the counter-electrode layer through the ion-conducting layer into the electrochromic layer. To change the electrochromic device from its heat reflective and light transmissive state to the heat and light transmissive state, the battery or other electrical power supply polarity is reversed and a low voltage potential is applied to the device whereby ions transfer into the electrochromic device to change the electrochromic layer to its heat transmissive state.
Upon the application of a voltage required for electron transfer, the positive ions could transfer to the outer electrode layers and interact with the indium-tin oxides within the layers to deplete the device of requisite positive ions. The ions could also become exposed with the atmosphere about the device and irreversibly react with the atmospheric gases.
Upon long periods of continued use under such overvoltage conditions, the modulation of the electrochromic layers becomes reduced due to the loss of positive ions to the outer electrode layers and the surrounding environment.
One purpose of the instant invention accordingly is to provide a transparent ion-blocking layer between the active layers and the outer electrode layers to prevent irreversible transfer of ions to the outer electrode layers.